Inhibition of the mitogen activated protein (MAP) kinase cascade potentiates cell killing by low dose ionizing radiation in A431 human squamous carcinoma cells

Dual effects of active ERK in cancer: A potential target for enhancing radiosensitivity

Ionizing radiation (IR) is an important cancer treatment approach. However, radioresistance eventually occurs, resulting in poor outcomes in patients with cancer. Radioresistance is associated with multiple signaling pathways, particularly pro-survival signaling pathways. The extracellular signal-regulated kinase 1/2 (ERK1/2) cascade is an important signaling pathway that initiates several cellular processes and is regulated by various stimuli, including IR. Although numerous studies have demonstrated the pro-survival effects of active ERK, activation of ERK has also been associated with cell death, indicating that radiosensitization may occur by ERK stimulation. In this context, the present review describes the associations between ERK signaling, cancer and IR, and discusses the association between ERK and its pro-survival function in cancer cells, including stimuli, molecular mechanisms, clinical use of inhibitors and underlying limitations. Additionally, the present review introduces the view that active ERK may induce cell death, and describes the potential factors associated with this process. This review describes the various outcomes induced by active ERK to prompt future studies to aim to enhance radiosensitivity in the treatment of cancer.

Signaling alterations caused by drugs and autophagy

Autophagy is an evolutionary conserved process that recycles cellular materials in times of nutrient restriction to maintain viability. In cancer therapeutics, the role of autophagy in response to multi-kinase inhibitors, alone or when combined with histone deacetylase (HDAC) inhibitors acts, generally, to facilitate the killing of tumor cells. Furthermore, the formation of autophagosomes and subsequent degradation of their contents can reduce the expression of HDAC proteins themselves as well as of other signaling regulatory molecules such as protein chaperones and mutated RAS proteins. Reduced levels of HDAC6 causes the acetylation and inactivation of heat shock protein 90, and, together with reduced expression of the chaperones HSP70 and GRP78, generates a strong endoplasmic reticulum (ER) stress response. Prolonged intense ER stress signaling causes tumor cell death. Reduced expression of HDACs 1, 2 and 3 causes the levels of programed death ligand 1 (PD-L1) to decline and the expression of Class I MHCA to increase which correlates with elevated immunogenicity of the tumor cells in vivo. This review will specifically focus on the downstream implications that result from autophagic-degradation of HDACs, RAS and protein chaperones.

Phospho-ERK levels as predictors for chemotherapy of rectal carcinoma

Treatment of rectal cancer has been vastly improved by advances in surgery and radiochemotherapy but remains an important cause of morbidity and mortality worldwide. A particular problem is the lack of predictive markers that can help to individualize treatment. The growth- and apoptosis-regulating signaling molecules ERK 1 and 2 are important to cancer growth and progression. They are activated through phosphorylation, which is initiated by a cascade involving the EGF receptor and RAS as upstream regulators. Moreover, in vitro studies indicate that phospho-ERKs interfere with 5-fluorouracil-based chemotherapy. Recently, we showed that high levels of phospho-ERKs in rectal cancer cells predict poor responses to neoadjuvant (preoperative) radiochemotherapy. We now report that preoperative phospho-ERK levels also can subdivide high-risk rectal cancer patients into a favorable and a poor prognostic group with respect to recurrence-free survival. Importantly, phospho-ERK levels were of predictive significance only in high-risk patients, who received adjuvant (postoperative) chemotherapy, but not in high-risk patients not receiving such therapy. Our results suggest that high cancer cell levels of phospho-ERK predict poor responsiveness to both preoperative and postoperative chemotherapy of rectal cancer.

Inhibition of ERK1/2 or AKT Activity Equally Enhances Radiation Sensitization in B16F10 Cells

Background

The aim of the study was to evaluate the radiation sensitizing ability of ERK1/2, PI3K-AKT and JNK inhibitors in highly radiation resistant and metastatic B16F10 cells which carry wild-type Ras and Braf.

Methods

Mouse melanoma cell line B16F10 was exposed to 1.0, 2.0 and 3.0 Gy of electron beam radiation. Phosphorylated ERK1/2, AKT and JNK levels were estimated by ELISA. Cells were exposed to 2.0 and 3.0 Gy of radiation with or without prior pharmacological inhibition of ERK1/2, AKT as well as JNK pathways. Cell death induced by radiation as well as upon inhibition of these pathways was measured by TUNEL assay using flow cytometry.

Results

Exposure of B16F10 cells to 1.0, 2.0 and 3.0 Gy of electron beam irradiation triggered an increase in all the three phosphorylated proteins compared to sham-treated and control groups. B16F10 cells pre-treated with either ERK1/2 or AKT inhibitors equally enhanced radiation-induced cell death at 2.0 as well as 3.0 Gy (P < 0.001), while inhibition of JNK pathway increased radiation-induced cell death to a lesser extent. Interestingly combined inhibition of ERK1/2 or AKT pathways did not show additional cell death compared to individual ERK1/2 or AKT inhibition. This indicates that ERK1/2 or AKT mediates radiation resistance through common downstream molecules in B16F10 cells.

Conclusions

Even without activating mutations in Ras or Braf genes, ERK1/2 and AKT play a critical role in B16F10 cell survival upon radiation exposure and possibly act through common downstream effector/s.

MEK inhibitor GSK1120212-mediated radiosensitization of pancreatic cancer cells involves inhibition of DNA double-strand break repair pathways

PURPOSE

Over 90% of pancreatic adenocarcinoma PC express oncogenic mutant KRAS that constitutively activates the Raf-MEK-MAPK pathway conferring resistance to both radiation and chemotherapy. MEK inhibitors have shown promising anti-tumor responses in recent preclinical and clinical studies, and are currently being tested in combination with radiation in clinical trials. Here, we have evaluated the radiosensitizing potential of a novel MEK1/2 inhibitor GSK1120212 (GSK212,or trametinib) and evaluated whether MEK1/2 inhibition alters DNA repair mechanisms in multiple PC cell lines.

METHODS

Radiosensitization and DNA double-strand break (DSB) repair were evaluated by clonogenic assays, comet assay, nuclear foci formation (γH2AX, DNA-PK, 53BP1, BRCA1, and RAD51), and by functional GFP-reporter assays for homologous recombination (HR) and non-homologous end-joining (NHEJ). Expression and activation of DNA repair proteins were measured by immunoblotting.

RESULTS

GSK212 blocked ERK1/2 activity and radiosensitized multiple KRAS mutant PC cell lines. Prolonged pre-treatment with GSK212 for 24-48 hours was required to observe significant radiosensitization. GSK212 treatment resulted in delayed resolution of DNA damage by comet assays and persistent γH2AX nuclear foci. GSK212 treatment also resulted in altered BRCA1, RAD51, DNA-PK, and 53BP1 nuclear foci appearance and resolution after radiation. Using functional reporters, GSK212 caused repression of both HR and NHEJ repair activity. Moreover, GSK212 suppressed the expression and activation of a number of DSB repair pathway intermediates including BRCA1, DNA-PK, RAD51, RRM2, and Chk-1.

CONCLUSION

GSK212 confers radiosensitization to KRAS-driven PC cells by suppressing major DNA-DSB repair pathways. These data provide support for the combination of MEK1/2 inhibition and radiation in the treatment of PC.

Phospho-ERK1/2 levels in cancer cell nuclei predict responsiveness to radiochemotherapy of rectal adenocarcinoma

Locally advanced rectal adenocarcinoma is treated with radiochemotherapy (RCT) before surgery. The response to RCT is heterogeneous and consensus regarding reliable predictors is lacking. Since the ERK pathway is implicated in radioprotection, we examined pretreatment biopsies from 52 patients by immunohistochemistry for phosphorylated ERK (pERK). Immunostaining for pERK was considerably enhanced by use of alkaline demasking. Nuclear staining occurred in both cancer cells and stromal cells. Blind-coded sections were scored by 2 independent investigators. In patients showing no residual tumor after RCT (TRG1), staining for pERK in cancer, but not stromal, cell nuclei was significantly weaker than in patients showing a poor RCT response (TRG1 vs TRG4: p = 0.0001). Nuclear staining for pERK predicted poor responders, as illustrated by receiver operating characteristic curves with an area under curve of 0.86 (p = 0.0007) and also predicted downstaging (area under curve: 0.76; p = 0.01). A number of controls documented the specificity of the optimized staining method and results were confirmed with another pERK antibody. Thus, staining for pERK in cancer cell nuclei can predict the response to RCT and may help spare poor responders this treatment. These results also raise the question whether inhibitors of ERK activation may serve as response modifiers of RCT.

Localization of active, dually phosphorylated extracellular signal-regulated kinase 1 and 2 in colorectal cancer with or without activating BRAF and KRAS mutations

Colorectal cancers (CRC) often show activating mutations of the KRAS or BRAF genes, which stimulate the extracellular signal-regulated kinase (ERK) pathway, thus increasing cell proliferation and inhibiting apoptosis. However, immunohistochemical results on ERK activation in such tumors differ greatly. Recently, using a highly optimized immunohistochemical method, we obtained evidence that high levels of ERK activation in rectal adenocarcinomas were associated with resistance to radiochemotherapy. In order to determine whether KRAS and/or BRAF mutations correlate to immunohistochemically detectable increases in phosphorylation of ERK (pERK), we stained biopsies from 36 CRC patients with activating mutations in the BRAF gene (BRAFV600E: BRAF(m)), the KRAS gene (KRAS(m)) or in neither (BRAF/KRAS(n)) with this optimized method. Staining was scored in blind-coded specimens by two observers. Staining of stromal cells was used as a positive control. BRAF(m) or KRAS(m) tumors did not show higher staining scores than BRAF/KRAS(n) tumors. Although BRAFV600E staining occurred in over 90% of cancer cells in all 9 BRAF(m) tumors, 3 only showed staining for pERK in less than 10% of cancer cell nuclei. The same applied to 4 of the 14 KRAS(m) tumors. A phophorylation-insensitive antibody demonstrated that lack of pERK staining did not reflect defect expression of ERK1/2 protein. Thus, increased staining for pERK does not correlate to BRAF or KRAS mutations even with a highly optimized procedure. Further studies are required to determine whether this reflects differences in expression of counterregulatory molecules, including ERK phosphatases.

Transient delay of radiation-induced apoptosis by phorbol acetate

The mechanisms of interference of a model tumour promoter 12-O-tetra-decanoylphorbol-13-acetate (TPA) with radiation-induced apoptosis in human peripheral lymphocytes have been investigated. The cells were treated with TPA under various conditions and thereafter exposed to a single lethal dose of gamma radiation. Morphological and biochemical changes characteristic of apoptosis were followed up to 72 h of post-irradiation time. Acute exposure to low concentration of TPA resulted in delay in the onset of radiation-induced apoptosis (determined as morphological changes and rate of mitochondrial demise) by 24-48 h as compared to the irradiated, sham TPA-treated cells. The time course of this delay correlated well with confinement of the p53 protein to the cytoplasm and increase in bcl-2 levels at the nuclear periphery of irradiated cells. Our results indicate that confinement of p53 in the cytoplasm is one of the potential mechanisms by which TPA interferes with the process of radiation-induced apoptosis in human lymphocytes.

Mechanistic Insights into Molecular Targeting and Combined Modality Therapy for Aggressive, Localized Prostate Cancer

Radiation therapy (RT) is one of the mainstay treatments for prostate cancer (PCa). The potentially curative approaches can provide satisfactory results for many patients with non-metastatic PCa; however, a considerable number of individuals may present disease recurrence and die from the disease. Exploiting the rich molecular biology of PCa will provide insights into how the most resistant tumor cells can be eradicated to improve treatment outcomes. Important for this biology-driven individualized treatment is a robust selection procedure. The development of predictive biomarkers for RT efficacy is therefore of utmost importance for a clinically exploitable strategy to achieve tumor-specific radiosensitization. This review highlights the current status and possible opportunities in the modulation of four key processes to enhance radiation response in PCa by targeting the: (1) androgen signaling pathway; (2) hypoxic tumor cells and regions; (3) DNA damage response (DDR) pathway; and (4) abnormal extra-/intracell signaling pathways. In addition, we discuss how and which patients should be selected for biomarker-based clinical trials exploiting and validating these targeted treatment strategies with precision RT to improve cure rates in non-indolent, localized PCa.

EGFR monoclonal antibodies in locally advanced head and neck squamous cell carcinoma: What is their current role?

Treatment options for locally advanced squamous cell carcinoma of the head and neck (SCCHN) include either surgical resection followed by radiation or chemoradiation, or definitive chemoradiation for which single-agent cisplatin is the best studied and established. The increasing understanding of the molecular biology of SCCHN has led to an interest in the development of targeted therapies. The epidermal growth factor receptor (EGFR) is over-expressed in nearly 80-90% of cases of SCCHN and correlates with poor prognosis and resistance to radiation. Preclinical evidence showed that blocking EGFR restores radiation sensitivity and enhances cytotoxicity. This finding led to clinical trials evaluating this class of agents and the approval of cetuximab in combination with radiation for the treatment of locally advanced SCCHN. This review is focused on the anti-EGFR monoclonal antibodies and their role either with radiotherapy or chemoradiation in unresectable LA SCCHN.

Methylation status of IGFBP-3 as a useful clinical tool for deciding on a concomitant radiotherapy

The methylation status of the IGFBP-3 gene is strongly associated with cisplatin sensitivity in patients with non-small cell lung cancer (NSCLC). In this study, we found in vitro evidence that linked the presence of an unmethylated promoter with poor response to radiation. Our data also indicate that radiation might sensitize chemotherapy-resistant cells by reactivating IGFBP-3-expression through promoter demethylation, inactivating the PI3K/AKT pathway. We also explored the IGFBP-3 methylation effect on overall survival (OS) in a population of 40 NSCLC patients who received adjuvant therapy after R0 surgery. Our results indicate that patients harboring an unmethylated promoter could benefit more from a chemotherapy schedule alone than from a multimodality therapy involving radiotherapy and platinum-based treatments, increasing their OS by 2.5 y (p = .03). Our findings discard this epi-marker as a prognostic factor in a patient population without adjuvant therapy, indicating that radiotherapy does not improve survival for patients harboring an unmethylated IGFBP-3 promoter.

Role of the MAPK pathway in the observed bystander effect in lymphocytes co-cultured with macrophages irradiated with γ-rays or carbon ions

AIMS

The radiation-induced bystander effect (RIBE) has potential implications in cancer risks from space particle radiation; however, the mechanisms underlying RIBE are unclear. The role of the MAPK pathway in the RIBEs of different linear energy transfer (LET) was investigated.

MAIN METHODS

Human macrophage U937 cells were irradiated with γ-rays or carbon ions and then co-cultured with nonirradiated HMy2.CIR (HMy) lymphocytes for different periods. The activation of MAPK proteins and the generation of intracellular nitric oxide (NO) and reactive oxygen species (ROS) in the irradiated U937 cells were measured. Micronuclei (MN) formation in the HMy cells was applied to evaluate the bystander damage. Some U937 cells were pretreated with different MAPK inhibitors before irradiation.

KEY FINDINGS

Additional MN formation was induced in the HMy cells after co-culturing with irradiated U937 cells, and the yield of this bystander MN formation was dependent on the co-culture period with γ-ray irradiation but remained high after 1h of co-culture with carbon irradiation. Further investigations disclosed that the time response of the RIBEs had a relationship with LET, where ERK played a different role from JNK and p38 in regulating RIBEs by regulating the generation of the bystander signaling factors NO and ROS.

SIGNIFICANCE

The finding that the RIBE of high-LET radiation could persist for a much longer period than that of γ-rays implies that particle radiation during space flight could have a high risk of long-term harmful effects. An appropriate intervention targeting the MAPK pathway may have significant implications in reducing this risk.

Mitogen-activated protein kinases and their role in radiation response

Ionizing radiation, like a variety of other cellular stress factors, can activate or down-regulate multiple signaling pathways, leading to either increased cell death or increased cell proliferation. Modulation of the signaling process, however, depends on the cell type, radiation dose, and culture conditions. The mitogen-activated protein kinase (MAPK) pathway transduces signals from the cell membrane to the nucleus in response to a variety of different stimuli and participates in various intracellular signaling pathways that control a wide spectrum of cellular processes, including growth, differentiation, and stress responses, and is known to have a key role in cancer progression. Multiple signal transduction pathways stimulated by ionizing radiation are mediated by the MAPK superfamily including the extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAPK. The ERK pathway, activated by mitogenic stimuli such as growth factors, cytokines, and phorbol esters, plays a major role in regulating cell growth, survival, and differentiation. In contrast, JNK and p38 MAPK are weakly activated by growth factors but respond strongly to stress signals including tumor necrosis factor (TNF), interleukin-1, ionizing and ultraviolet radiation, hyperosmotic stress, and chemotherapeutic drugs. Activation of JNK and p38 MAPK by stress stimuli is strongly associated with apoptotic cell death. MAPK signaling is also known to potentially influence tumor cell radiosensitivity because of their activity associated with radiation-induced DNA damage response. This review will discuss the MAPK signaling pathways and their roles in cellular radiation responses.

Bile acid accelerates erbB2-induced pro-tumorigenic activities in biliary tract cancer

Although very few studies have addressed the molecular and cellular mechanisms underlying the development of biliary tract cancer (BTC), several lines of evidence suggest a role for the erbB receptor family. Overexpression and activation of erbB2 has been reported in a significant percentage of human BTC. Further, we previously reported that overexpression of erbB2 basal epithelial cells of the biliary tract (BK5.erbB2 mouse) led to the development of BTC. However, the mechanisms by which erbB2 overexpression led to the spontaneous development of tumors specifically in the biliary tract are not completely understood. The goals of the current study were to (1) determine whether a cooperative relationship between bile acid exposure and erbB2 activation exists during biliary tract carcinogenesis and (2) to characterize the mechanism(s) underlying bile acid-mediated biliary tract carcinogenesis in cells with activated erbB2. In this study, we demonstrated that the secondary conjugated bile acid, taurochenodeoxycholic acid (TCDC), increased proliferation of primary cultured gallbladder epithelial cells from BK5.erbB2 mice and human BTC cells. TCDC treatment activated EGFR/erbB2 and downstream signaling molecules in both primary cultured cells and human BTC cells. TCDC also increased the expression of epidermal growth factor receptor (EGFR) ligands and TACE activity in human BTC cells. Inhibition of src activation led to attenuation of bile-induced upregulation of TACE activity as well as signaling through the EGFR/erbB2, suggesting that during the development of BTC erbB2 overexpression/activation accelerates the bile acid-induced signaling cascade: bile acid → src → TACE → EGFR/erbB2 → downstream signaling. We also provide direct evidence that bile acids possess tumor promoting capacity in epithelial cells overexpressing erbB2 using the two-stage skin carcinogenesis model. Collectively these findings suggest cooperative roles for bile acid and erbB2 activation in epithelial cell proliferation; bile acid appears to accelerate erbB2-induced pro-tumorigenic activities in the biliary tract and skin.

Targeted therapy against EGFR and VEGFR using ZD6474 enhances the therapeutic potential of UV-B phototherapy in breast cancer cells

Background

The hypoxic environment of tumor region stimulated the up regulation of growth factors responsible for angiogenesis and tumor proliferation. Thus, targeting the tumor vasculature along with the proliferation by dual tyrosine kinase inhibitor may be the efficient way of treating advanced breast cancers, which can be further enhanced by combining with radiotherapy. However, the effectiveness of radiotherapy may be severely compromised by toxicities and tumor resistance due to radiation-induced adaptive response contributing to recurrence and metastases of breast cancer. The rational of using ZD6474 is to evaluate the feasibility and efficacy of combined VEGFR2 and EGFR targeting with concurrent targeted and localized UV-B phototherapy in vitro breast cancer cells with the anticipation to cure skin lesions infiltrated with breast cancer cells.

Materials and methods

Breast cancer cells were exposed to UV-B and ZD6474 and the cell viability, apoptosis, invasion and motility studies were conducted for the combinatorial effect. Graphs and statistical analyses were performed using Graph Pad Prism 5.0.

Results

ZD6474 and UV-B decreased cell viability in breast cancers in combinatorial manner without affecting the normal human mammary epithelial cells. ZD6474 inhibited cyclin E expression and induced p53 expression when combined with UV-B. It activated stress induced mitochondrial pathway by inducing translocation of bax and cytochrome-c. The combination of ZD6474 with UV-B vs. either agent alone also more potently down-regulated the anti-apoptotic bcl-2 protein, up-regulated pro-apoptotic signaling events involving expression of bax, activation of caspase-3 and caspase-7 proteins, and induced poly (ADP-ribose) polymerase resulting in apoptosis. ZD6474 combined with UV-B inhibited invasion of breast cancer cells in vitro as compared to either single agent, indicating a potential involvement of pro-angiogenic growth factors in regulating the altered expression and reorganization of cytoskeletal proteins in combinatorial treated breast cancer cells. Involvement of combination therapy in reducing the expression of matrix metalloprotease was also observed.

Conclusions

Collectively, our studies indicate that incorporating an anti-EGFR plus VEGFR strategy (ZD6474) with phototherapy (UV-B), an alternative approach to the ongoing conventional radiotherapy for the treatment of infiltrating metastatic breast cancer cells in the skin and for locally recurrence breast cancer than either approach alone.

Lung cancer cells that survive ionizing radiation show increased integrin α2β1- and EGFR-dependent invasiveness

Ionizing radiation (IR)-enhanced tumor invasiveness is emerging as a contributor to the limited benefit of radiotherapy; however, its mechanism is still unclear. We previously showed that subcloned lung adenocarcinoma A549 cells (P cells), which survived 10 Gy IR (IR cells), acquired high invasiveness in vitro. Here, we tried to identify the mechanism by which IR cells increase their invasiveness by examining altered gene expression and signaling pathways in IR cells compared with those in P cells. To simulate the microenvironment in vivo, cells were embedded in a three-dimensional (3D) collagen type I gel, in which the IR cells were elongated, while the P cells were spherical. The integrin expression pattern was surveyed, and expression levels of the integrin α2 and β1 subunits were significantly elevated in IR cells. Knockdown of α2 expression or functional blockade of integrin α2β1 resulted in a round morphology of IR cells, and abrogated their invasion in the collagen matrix, suggesting the molecule's essential role in cell spread and invasion in 3D collagen. Epidermal growth factor receptor (EGFR) also presented enhanced expression and activation in IR cells. Treatment with EGFR tyrosine kinase inhibitor, PD168393, decreased the ratio of elongated cells and cell invasiveness. Signaling molecules, including extracellular signal-regulated kinase-1/2 (Erk1/2) and Akt, exhibited higher activation in IR cells. Inhibition of Akt activation by treating with phosphoinositide 3-kinase (PI3K) inhibitor LY294002 decreased IR cell invasion, whereas inhibition of Erk1/2 activation by mitogen-activated protein kinase kinase (MEK) inhibitor U0126 did not. Our results show that integrin α2β1 and EGFR cooperatively promote higher invasiveness of IR-survived lung cancer cells, mediated in part by the PI3K/Akt signaling pathway, and might serve as alternative targets in combination with radiotherapy.

MEK2 regulates ribonucleotide reductase activity through functional interaction with ribonucleotide reductase small subunit p53R2

The p53R2 protein, a newly identified member of the ribonucleotide reductase family that provides nucleotides for DNA damage repair, is directly regulated by p53. We show that p53R2 is also regulated by a MEK2 (ERK kinase 2/MAP kinase kinase 2)-dependent pathway. Increased MEK1/2 phosphorylation by serum stimulation coincided with an increase in the RNR activity in U2OS and H1299 cells. The inhibition of MEK2 activity, either by treatment with a MEK inhibitor or by transfection with MEK2 siRNA, dramatically decreased the serum-stimulated RNR activity. Moreover, p53R2 siRNA, but not R2 siRNA, significantly inhibits serum-stimulated RNR activity, indicating that p53R2 is specifically regulated by a MEK2-dependent pathway. Co-immunoprecipitation analyses revealed that the MEK2 segment comprising amino acids 65-171 is critical for p53R2-MEK2 interaction, and the binding domain of MEK2 is required for MEK2-mediated increased RNR activity. Phosphorylation of MEK1/2 was greatly augmented by ionizing radiation, and RNR activity was concurrently increased. Ionizing radiation-induced RNR activity was markedly attenuated by transfection of MEK2 or p53R2 siRNA, but not R2 siRNA. These data show that MEK2 is an endogenous regulator of p53R2 and suggest that MEK2 may associate with p53R2 and upregulate its activity.

Measurement of hepatic protein fractional synthetic rate with stable isotope labeling technique in thapsigargin stressed HepG2 cells

Severe burn-induced liver damage and dysfunction is associated with endoplasmic reticulum (ER) stress. ER stress has been shown to regulate global protein synthesis. In the current study, we induced ER stress in vitro and estimated the effect of ER stress on hepatic protein synthesis. The aim was two-fold: (1) to establish an in vitro model to isotopically measure hepatic protein synthesis and (2) to evaluate protein fractional synthetic rate (FSR) in response to ER stress. Human hepatocellular carcinoma cells (HepG2) were cultured in medium supplemented with stable isotopes 1,2-¹³C₂-glycine and L-[ring-¹³C₆]phenylalanine. ER stress was induced by exposing the cells to 100 nM of thapsigargin (TG). Cell content was collected from day 0 to 14. Alterations in cytosolic calcium were measured by calcium imaging and ER stress markers were confirmed by Western blotting. The precursor and product enrichments were detected by GC-MS analysis for FSR calculation. We found that the hepatic protein FSR were 0.97±0.02 and 0.99±0.05%/hr calculated from 1,2-¹³C₂-glycine and L-[ring-¹³C₆]phenylalanine, respectively. TG depleted ER calcium stores and induced ER stress by upregulating p-IRE-1 and Bip. FSR dramatically decreased to 0.68±0.03 and 0.60±0.06%/hr in the TG treatment group (p<0.05, vs. control). TG-induced ER stress inhibited hepatic protein synthesis. The stable isotope tracer incorporation technique is a useful method for studying the effects of ER stress on hepatic protein synthesis.

Role and expression of FRS2 and FRS3 in prostate cancer

Background

FGF receptor substrates (FRS2 and FRS3) are key adaptor proteins that mediate FGF-FGFR signalling in benign as well as malignant tissue. Here we investigated FRS2 and FRS3 as a means of disrupting global FGF signalling in prostate cancer.

Methods

FRS2 and FRS3 manipulation was investigated in vitro using over-expression, knockdown and functional assays. FRS2 and FRS3 expression was profiled in cell lines and clinical tumors of different grades.

Results

In a panel of cell lines we observed ubiquitous FRS2 and FRS3 transcript and protein expression in both benign and malignant cells. We next tested functional redundancy of FRS2 and FRS3 in prostate cancer cells. In DU145 cells, specific FRS2 suppression inhibited FGF induced signalling. This effect was not apparent in cells stably over-expressing FRS3. Indeed FRS3 over-expression resulted in enhanced proliferation (p = 0.005) compared to control cells. Given this functional redundancy, we tested the therapeutic principle of dual targeting of FRS2 and FRS3 in prostate cancer. Co-suppression of FRS2 and FRS3 significantly inhibited ERK activation with a concomitant reduction in cell proliferation (p < 0.05), migration and invasion (p < 0.05). Synchronous knockdown of FRS2 and FRS3 with exposure to cytotoxic irradiation resulted in a significant reduction in prostate cancer cell survival compared to irradiation alone (p < 0.05). Importantly, this synergistic effect was not observed in benign cells. Finally, we investigated expression of FRS2 and FRS3 transcript in a cohort of micro-dissected tumors of different grades as well as by immunohistochemistry in clinical biopsies. Here, we did not observe any difference in expression between benign and malignant biopsies.

Conclusions

These results suggest functional overlap of FRS2 and FRS3 in mediating mitogenic FGF signalling in the prostate. FRS2 and FRS3 are not over-expressed in tumours but targeted dual inhibition may selectively adversely affect malignant but not benign prostate cells.

Regulation of Caenorhabditis elegans p53/CEP-1-dependent germ cell apoptosis by Ras/MAPK signaling

Maintaining genome stability in the germline is thought to be an evolutionarily ancient role of the p53 family. The sole Caenorhabditis elegans p53 family member CEP-1 is required for apoptosis induction in meiotic, late-stage pachytene germ cells in response to DNA damage and meiotic recombination failure. In an unbiased genetic screen for negative regulators of CEP-1, we found that increased activation of the C. elegans ERK orthologue MPK-1, resulting from either loss of the lip-1 phosphatase or activation of let-60 Ras, results in enhanced cep-1-dependent DNA damage induced apoptosis. We further show that MPK-1 is required for DNA damage-induced germ cell apoptosis. We provide evidence that MPK-1 signaling regulates the apoptotic competency of germ cells by restricting CEP-1 protein expression to cells in late pachytene. Restricting CEP-1 expression to cells in late pachytene is thought to ensure that apoptosis doesn't occur in earlier-stage cells where meiotic recombination occurs. MPK-1 signaling regulates CEP-1 expression in part by regulating the levels of GLD-1, a translational repressor of CEP-1, but also via a GLD-1-independent mechanism. In addition, we show that MPK-1 is phosphorylated and activated upon ionising radiation (IR) in late pachytene germ cells and that MPK-1-dependent CEP-1 activation may be in part direct, as these two proteins interact in a yeast two-hybrid assay. In summary, we report our novel finding that MAP kinase signaling controls CEP-1-dependent apoptosis by several different pathways that converge on CEP-1. Since apoptosis is also restricted to pachytene stage cells in mammalian germlines, analogous mechanisms regulating p53 family members are likely to be conserved throughout evolution.

Simultaneous exposure of transformed cells to SRC family inhibitors and CHK1 inhibitors causes cell death

The present studies were initiated to determine in greater molecular detail the regulation of CHK1 inhibitor lethality in transfected and infected breast cancer cells and using genetic models of transformed fibrobalsts. Multiple MEK1/2 inhibitors (PD184352, AZD6244 (ARRY-142886)) interacted with multiple CHK1 inhibitors (UCN-01 (7-hydroxystaurosporine), AZD7762) to kill mammary carcinoma cells and transformed fibroblasts. In transformed cells, CHK1 inhibitor -induced activation of ERK1/2 was dependent upon activation of SRC family non-receptor tyrosine kinases as judged by use of multiple SRC kinase inhibitors (PP2, Dasatinib; AZD0530), use of SRC/FYN/YES deleted transformed fibroblasts or by expression of dominant negative SRC. Cell killing by SRC family kinase inhibitors and CHK1 inhibitors was abolished in BAX/BAK -/- transformed fibroblasts and suppressed by over expression of BCL-XL. Treatment of cells with BCL-2/BCL-XL antagonists promoted SRC inhibitor + CHK1 inhibitor -induced lethality in a BAX/BAK-dependent fashion. Treatment of cells with [SRC + CHK1] inhibitors radio-sensitized tumor cells. These findings argue that multiple inhibitors of the SRC-RAS-MEK pathway interact with multiple CHK1 inhibitors to kill transformed cells.

Activation of mitogen-activated protein kinase extracellular signal-related kinase in head and neck squamous cell carcinomas after irradiation as part of a rescue mechanism

BACKGROUND

Irradiation plays a pivotal role in head and neck squamous cell carcinoma (HNSCC) treatment. However, especially recurrent tumors frequently show increased radioresistance. We analyzed irradiation-stimulated mitogen-activated protein kinase (MAPK) signaling pathways to define cellular rescue mechanisms.

METHODS

Irradiated HNSCC cells were screened for MAPK activation and results were confirmed and refined by functional analyses. Extracellular signal-regulated kinase (ERK) inhibitor U0126 application enabled us to specify postradiogenic cellular responses. Vascular endothelial growth factor (VEGF) levels were analyzed additionally.

RESULTS

We observed a pronounced and time-dependent ERK stimulation. Pathway inhibition resulted in decreased radioresistance. Likewise, we found a decrease of VEGF release after inhibitor treatment. ERK activation was confirmed in xenotransplants showing elevated postradiogenic phospho-ERK (pERK) and VEGF levels.

CONCLUSIONS

Our data give evidence for induction of ERK and successive VEGF release in HNSCC during radiotherapy, which might be partially explained by autoregulated cytoprotection maintained by pERK and potentially VEGF. In conclusion, targeting the ERK-VEGF axis might enhance the efficiency of radiotherapy.

Low-dose ionizing radiation effects on differentiation of HL-60 cells

The biological effects of low-dose radiation have attracted attention, but data are currently insufficient to fully understand the beneficial role of the phenomenon. In the present study, we have investigated the effects of low doses of gamma-irradiation alone and in combination with all-trans-retinoic acid (RA) on proliferation, apoptosis and differentiation of the human promyelocytic leukemia HL-60 cells. Changes in cell behavior and protein expression were determined with the use of light and fluorescent microscopy, immunocytochemical and Western blot analysis. Low-dose irradiation with 1–100 cGy caused a dose-dependent inhibition of HL-60 cell proliferation, and induced apoptosis and differentiation to granulocytes with an increase in the number of CD15-positive cells. Pre-irradiation with 1–100 cGy for 24 h before treatment with RA promoted apoptosis but did not impair RA-induced differentiation. Both processes were associated with a decrease in the expression of the proliferating cell nuclear antigen (PCNA), BCL-2, c-MYC, and changes in both cytosolic and nuclear levels of protein tyrosine-phosphorylation as well as protein kinase C alpha or beta isoforms. These results demonstrate the beneficial role of low-dose irradiation in modulating leukemia cell proliferation, differentiation and apoptosis.

Effect of radiation on vascular endothelial growth factor expression in the C2 canine mastocytoma cell line

OBJECTIVE

To establish the radiosensitivity and effect of irradiation on vascular endothelial growth factor (VEGF) and VEGF receptor (VEGFR) expression in the canine mastocytoma cell line C2.

SAMPLE POPULATION

Canine mastocytoma cell line C2.

PROCEDURES

C2 cells were irradiated with single doses of 2, 4, 6, and 8 Gy. The 3-(4, 5-di-methyl-2-thiazolyl)-2, 5-diphenyl-2H-tetrazolium bromide assay and proliferation assays with (methyl-hydrogen 3) thymidine were used for radiosensitivity experiments. Expression of VEGFR was determined via flow cytometry and apoptotic rate via annexin assay. Human and canine VEGF ELISA kits were evaluated in crossover assay experiments, and the canine kit was used thereafter.

RESULTS

C2 cells secreted VEGF constitutively. Radiation did not induce a significant increase in VEGF secretion, regardless of radiation dose. Consistently, radiation did not up-regulate VEGFR. Cell survival rates decreased in a dose-dependent manner. The apoptotic cell fraction had a dose-dependent increase that reached its maximum 24 to 48 hours after radiation.

CONCLUSIONS AND CLINICAL RELEVANCE

The C2 cell line was radiosensitive, and a fraction (up to 40%) of cells died via apoptosis in a dose-dependent manner. In response to radiation, C2 cells did not upregulate VEGF production or VEGFR. Further studies are needed to determine whether tumor control could be improved by combining radiotherapy with VEGFR inhibitors or apoptosis-modulating agents.

A phase I/II trial of gefitinib given concurrently with radiotherapy in patients with nonmetastatic prostate cancer

PURPOSE

To estimate the safety and tolerability of daily administration of 250 mg of gefitinib given concurrently with three-dimensional conformal radiotherapy for patients with nonmetastatic prostate cancer.

METHODS AND MATERIALS

A total of 42 patients with T2-T3N0M0 tumors were treated in a nonrandomized single-center study. A prostate-specific antigen (PSA) level of <20 and a good performance status (WHO, 0-1) were required. Adjuvant or neoadjuvant hormone treatments were not allowed. A daily regimen of 250 mg of gefitinib was started 1 week before radiation therapy began and lasted for the duration of radiation therapy. A dose of 50.4 Gy (1.8 Gy/day) was administered to the tumor, prostate, and seminal vesicles, followed by a 22-Gy booster (2 Gy/day) for a total dose of 72.4 Gy. Correlative studies included analysis of epidermal growth factor receptor (EGFR), EGFRvIII, and phosphorylated EGFR in tumors and tumor necrosis factor, interleukin-1alpha (IL-1alpha), and IL-6 in serum.

RESULTS

Maximum tolerated dose was not reached in phase I (12 patients), and 30 additional patients were treated in phase II. Thirty (71.4%) patients completed trial medication. Dose-limiting toxicities were recorded for 16 (38.1%) patients, the most common of which was a grade 3 to 4 increase in transaminase (6 patients). After a median follow-up of 38 months, there were no deaths due to prostate cancer. The estimated PSA relapse-free survival rate at 4 years (Kaplan-Meier) was 97%, the salvage therapy-free survival rate was 91%, and the overall survival rate was 87%. These figures compared favorably with those of matched patients treated with radiation only at higher doses.

CONCLUSIONS

The combination of gefitinib and radiation is reasonably well tolerated and has promising activity against nonmetastatic prostate cancer.

The mitogen-activated protein/extracellular signal-regulated kinase kinase 1/2 inhibitor AZD6244 (ARRY-142886) enhances the radiation responsiveness of lung and colorectal tumor xenografts

PURPOSE

Novel molecularly targeted agents, given in combination with radiotherapy, have the potential to increase tumor response rates and the survival of patients with lung cancer. AZD6244 is a potent and selective inhibitor of mitogen-activated protein kinase (MAPK) kinase 1/2 (MEK1/2), a critical enzyme within the MAPK/extracellular signal-regulated kinase (ERK) signaling pathway that regulates the proliferation and survival of tumor cells.

EXPERIMENTAL DESIGN

This study examined the potential benefit of combining AZD6244 with fractionated radiotherapy using human lung and colon carcinoma xenograft models.

RESULTS

AZD6244 reduced ERK phosphorylation in Calu-6 lung cancer cells in vitro. Administration of AZD6244 for 10 days (25 mg/kg twice daily p.o.) inhibited the tumor growth of Calu-6 xenografts, with regrowth occurring on cessation of drug treatment. When fractionated tumor-localized radiotherapy (5 x 2 Gy) was combined with AZD6244 treatment, the tumor growth delay was enhanced significantly when compared with either modality alone, and this effect was also seen in a colon tumor model. We examined the effect of inhibiting MEK1/2 on the molecular responses to hypoxia, a potential interaction that could contribute to radioresponsiveness. AZD6244 reduced hypoxia-inducible factor-specific transactivation in vivo, shown using Calu-6 dual clone cells that stably express a Firefly luciferase gene under the control of a hypoxia-driven promoter. Furthermore, hypoxia-inducible factor-1 alpha, GLUT-1, and vascular endothelial growth factor levels were reduced by AZD6244, and there was a significant decrease in vascular perfusion in the tumors given combination treatment when compared with the other treatment groups.

CONCLUSIONS

These data provide support for the clinical development of AZD6244 in combination with radiotherapy and indicate a potential role for AZD6244 in inhibiting the tumor hypoxia response.

Synergistic combinations of signaling pathway inhibitors: mechanisms for improved cancer therapy

Cancer cells contain multiple signal transduction pathways whose activities are frequently elevated due to their transformation, and that are often activated following exposure to established cytotoxic therapies including ionizing radiation and chemical DNA damaging agents. Many pathways activated in response to transformation or toxic stresses promote cell growth and invasion and counteract the processes of cell death. As a result of these findings many drugs, predominantly protein and lipid kinase inhibitors, of varying specificities, have been developed to block signaling by cell survival pathways in the hope of killing tumor cells and sensitizing them to toxic therapies. Unfortunately, due to the plasticity of signaling processes within a tumor cell, inhibition of any one growth factor receptor or signaling pathway frequently has only modest long-term effects on cancer cell viability, tumor growth, and patient survival. As a result of this realization, a greater emphasis has begun to be placed on rational combinations of drugs that simultaneously inhibit multiple inter-linked signal transduction/survival pathways. This, it is hoped, will limit the ability of tumor cells to adapt and survive because the activity within multiple parallel survival signaling pathways has been reduced. This review will discuss some of the approaches that have been taken to combine signal transduction modulatory agents to achieve enhanced tumor cell killing.

Transient exposure of carcinoma cells to RAS/MEK inhibitors and UCN-01 causes cell death in vitro and in vivo

The present studies were initiated to determine in greater molecular detail how MEK1/2 inhibitors [PD184352 and AZD6244 (ARRY-142886)] interact with UCN-01 (7-hydroxystaurosporine) to kill mammary carcinoma cells in vitro and radiosensitize mammary tumors in vitro and in vivo and whether farnesyl transferase inhibitors interact with UCN-01 to kill mammary carcinoma cells in vitro and in vivo. Expression of constitutively activated MEK1 EE or molecular suppression of JNK and p38 pathway signaling blocked MEK1/2 inhibitor and UCN-01 lethality, effects dependent on the expression of BAX, BAK, and, to a lesser extent, BIM and BID. In vitro colony formation studies showed that UCN-01 interacted synergistically with the MEK1/2 inhibitors PD184352 or AZD6244 and the farnesyl transferase inhibitors FTI277 and R115,777 to kill human mammary carcinoma cells. Athymic mice carrying approximately 100 mm(3) MDA-MB-231 cell tumors were subjected to a 2-day exposure of either vehicle, R115,777 (100 mg/kg), the MEK1/2 inhibitor PD184352 (25 mg/kg), UCN-01 (0.2 mg/kg), or either of the drugs in combination with UCN-01. Transient exposure of tumors to R115,777, PD184352, or UCN-01 did not significantly alter tumor growth rate or the mean tumor volume in vivo approximately 15 to 30 days after drug administration. In contrast, combined treatment with R115,777 and UCN-01 or with PD184352 and UCN-01 significantly reduced tumor growth. Tumor cells isolated after combined drug exposure exhibited a significantly greater reduction in plating efficiency using ex vivo colony formation assays than tumor cells that were exposed to either drug individually. Irradiation of mammary tumors after drug treatment, but not before or during treatment, significantly enhanced the lethal effects of UCN-01 and MEK1/2 inhibitor treatment. These findings argue that UCN-01 and multiple inhibitors of the RAS-MEK pathway have the potential to suppress mammary tumor growth, and to interact with radiation, in vitro and in vivo.

Effect of nitric oxide donor and gamma irradiation on modifications of ERK and JNK in murine peritoneal macrophages

Mitogen activated protein kinases (MAPKs) play an important role in activation, differentiation and proliferation of macrophages. Macrophages, upon activation, produce large amounts of nitric oxide that inhibit the growth of variety of microorganisms and tumor cells. This nitric oxide which is known to interfere with tyrosine phosphorylation may result in changes in the pattern of activation of MAPKs. In a previous study we have found that tyrosine phosphorylation of MAPKs was completely abolished in the presence of nitric oxide donor and radiation but this did not affect the function of macrophages. In this study the other post translational modifications namely nitration and ubiquitination of JNK and ERK have been looked at. Both ERK and JNK were found to be nitrated. However, there was no increase in ubiquitination of ERK and JNK, indicating that ubiquitination, in this case was not a natural consequence of nitration and may serve in signaling. Additionally, when the nitration was extensive, phosphorylation was also inhibited. The activation of substrates of ERK and JNK were looked at to determine the consequences of such modifications. Inhibition of phosphorylation and extensive nitration of JNK did not prevent activation of its substrate, c-jun. This study indicates that ERK and JNK may be under regulation by different type of modifications in macrophages.

Effect of nitric oxide donor and gamma irradiation on MAPK signaling in murine peritoneal macrophages

Irradiation (IR) of cells is known to activate enzymes of mitogen activated protein kinase (MAPK) family. These are known to be involved in cellular response to stress and are determinants of cell death or survival. When radiotherapy is delivered to malignant cells, macrophages, being radioresistant, survive, get activated, and produce large amounts of nitric oxide. As a result of activation they recognize and phagocytose tumor and normal cell apoptotic bodies leading to tumor regression. In this study, the MAPK signaling in peritoneal macrophages was investigated which plays an important role in its various functions, in an environment which is predominantly nitric oxide, as is after IR. The behavior of macrophages in such an environment was also looked at. The three MAPK (ERK1/2, p38, and JNK) respond differently to Sodium nitroprusside (SNP) alone or IR alone. All the three were activated following IR but only JNK was activated following SNP treatment. Surprisingly, when both the stresses were given simultaneously or one after the other, this differential response was lost and there was a complete inhibition of phosphorylation of all the three MAPKs, irrespective of the order of the two insults (IR and SNP). The noteworthy observation was that despite the complete inhibition of MAPK signaling there was no effect on either the viability or the phagocytic efficiency of peritoneal macrophages.

Approaches for monitoring signal transduction changes in normal and cancer cells

This chapter will describe methods to assess the activities of protein kinases. Initial studies in the 1950s and 1960s in the field of glucose metabolism examined the activities of several highly specific protein and carbohydrate kinases in cell lysates or isolated cell fractions. As more protein kinases were discovered in the 1980s and 1990s, coupled with the development of immunoprecipitating antibodies, in vitro kinase assays of isolated kinase proteins using gamma-32P ATP became a standard procedure. In the 1990s, antibodies were developed that recognize specific sites of regulatory phosphorylation on a variety of protein kinases (phospho-specific antibodies), which have been used to assess kinase activity indirectly through immunoblotting. In this chapter, Methodologies to perform immune complex protein kinase assays and immunoblotting using phospho-specific antibodies against regulatory sites of phosphorylation in protein kinases will be described. The strengths and weaknesses of each approach in determining protein kinase activity will also be discussed.

Radiosensitization and modulation of p44/42 mitogen-activated protein kinase by 2-Methoxyestradiol in prostate cancer models

2-Methoxyestradiol (2ME2) is an endogenous estradiol metabolite that inhibits microtubule polymerization, tumor growth, and angiogenesis. Because prostate cancer is often treated with radiotherapy, and 2ME2 has shown efficacy as a single agent against human prostate carcinoma, we evaluated 2ME2 as a potential radiosensitizer in prostate cancer models. A dose-dependent decrease in mitogen-activated protein kinase phosphorylation was observed in human PC3 prostate cancer cells treated with 2ME2 for 18 h. This decrease correlated with in vitro radiosensitization measured by clonogenic assays, and these effects were blocked by the expression of constitutively active MEK. Male nude mice with subcutaneous PC3 xenografts in the hind leg were treated with 2ME2 (75 mg/kg) p.o. for 5 days, and 2 Gy radiation fractions were delivered each day at 4 h after drug treatment. A statistically significant super-additive effect between radiation and 2ME2 was observed in this subcutaneous model, using analysis of within-animal slopes. A PC-3M orthotopic model was also used, with bioluminescence imaging as an end point. PC-3M cells stably expressing the luciferase gene were surgically implanted into the prostates of male nude mice. Mice were given oral doses of 2ME2 (75 mg/kg), with radiation fractions (3 Gy) delivered 4 h later. Mice were then imaged weekly for 4 to 5 weeks with a Xenogen system. A significant super-additive effect was also observed in the orthotopic model. These data show that 2ME2 is an effective radiosensitizing agent against human prostate cancer xenografts, and that the mechanism may involve a decrease in mitogen-activated protein kinase phosphorylation by 2ME2.

Low-dose of ionizing radiation enhances cell proliferation via transient ERK1/2 and p38 activation in normal human lung fibroblasts

This study shows the human cellular responses and the mechanism of low-dose ionizing radiation in CCD 18 Lu cells, which are derived from normal human lung fibroblasts. Cell proliferation and viability assay were measured for the cells following gamma-irradiation using trypan blue, BrdU incorporation, and Wst-1 assay. We also examined genotoxicity using a micronuclei formation assay. The activation of the MAPKs pathway was determined by Western blot analysis, and the siRNA system was used to inhibit the expression of ERK1/2 and p38. We found that 0.05 Gy of ionizing radiation stimulated cell proliferation and did not change Micronuclei frequencies. In addition, 0.05 Gy of ionizing radiation activated ERK1/2 and p38, but did not activate JNK1/2 in cells. A specific ERK1/2 inhibitor, U0126, decreased the phosphorylation of ERK1/2 proteins induced by 0.05 Gy of ionizing radiation, and a similar suppressive effect was observed with a p38 inhibitor, PD169316. Suppression of ERK1/2 and p38 phosphorylation with these inhibitors decreased cell proliferation, which was stimulated by 0.05 Gy of ionizing radiation. Furthermore, downregulation of ERK1/2 and p38 expression using siRNA blocked the cell proliferation that had been increased by 0.05 Gy of ionizing radiation. These results suggest that 0.05 Gy of ionizing radiation enhances cell proliferation through the activation of ERK1/2 and p38 in normal human lung fibroblasts.

Low-Dose BBR3610 Toxicity in Colon Cancer Cells Is p53-Independent and Enhanced by Inhibition of Epidermal Growth Factor Receptor (ERBB1)-Phosphatidyl Inositol 3 Kinase Signaling

We have examined the mechanisms by which the multinuclear platinum chemotherapeutic BBR3610 kills human colon cancer cells. BBR3610 more efficiently killed HCT116, DLD1, SW480, and HT29 cells than BBR3464, cisplatin, or oxaliplatin. The amount of platinum uptake per cell and its incorporation into DNA were identical for BBR3464 and BBR3610. BBR3610 lethality (IC(75)) was unaltered comparing HCT116 wild-type and p53-/- cells, was reduced in p21-/- cells, and was enhanced in K-RAS D13 null cells. Small molecule or molecular inhibition of epidermal growth factor receptor (ERBB1) or phosphatidyl inositol 3 kinase (PI3K) enhanced BBR3610 toxicity in HCT116, DLD1, and SW480 cells. Small molecule or molecular inhibition of caspase 8 function abolished the toxicity of BBR3610 and of BBR3610 + ERBB1 inhibitor treatments, whereas inhibition of caspase 9 suppressed the ability of ERBB1 inhibitors to enhance BBR3610 lethality. Treatment with BBR3610 reduced AKT activity; the expression of dominant-negative AKT enhanced and expression of constitutively active AKT suppressed, respectively, the toxicity of BBR3610 and of BBR3610 + ERBB1 inhibitor treatments. Treatment with BBR3610 reduced expression of c-FLIP-s and MCL-1, levels that were maintained in cells expressing constitutively active AKT. Overexpression of c-FLIP-s or loss of BID function suppressed BBR3610 toxicity, whereas overexpression of XIAP or Bcl-xL suppressed the potentiation of cell killing by ERBB1 inhibitors. Collectively, our data argue that BBR3610 promotes cell killing via a caspase 8-dependent mechanism, which can be enhanced by ERBB1/PI3K inhibitors that promote additional BBR3610-dependent cell killing via activation of BAX and caspase 9.

MAP kinases: Differential activation following in vivo and ex vivo irradiation

Mitogen activated protein kinases (MAPK) play a critical role in controlling cell survival and repopulation following exposure to ionising radiation. Most investigations on these pathways have been done using cultured cells or by ex vivo treatments. The present study was carried out to determine whether the response of MAPKs in mouse lymphocytes differs following in vivo and ex vivo irradiation with 60Co gamma-rays. We observed that ex vivo treatment resulted in a very significant decrease in the activated p44/42 and p38 MAPK as compared to in vivo. However, stress activated protein kinase (SAPK) response showed no significant difference between in vivo and ex vivo treatments. These observations point towards the differences in response elicited when the treatment is given in vivo as compared to in vitro. Therefore the findings reported from in vitro or ex vivo treatments should be treated with caution especially if it has to be clinically applied.

Effect of downregulation of survivin expression on radiosensitivity of human epidermoid carcinoma cells

PURPOSE

The expression of survivin, a member of the inhibitor-of-apoptosis protein family, is elevated in many types of human cancer. High survivin expression has been associated with poor patient prognosis and tumor resistance to chemotherapy and radiotherapy. The purpose of this study was to compare the radiosensitizing effects of five agents that target survivin on their relative ability to downregulate survivin expression.

METHODS AND MATERIALS

The human epidermoid carcinoma cell line A431 was treated with adenoviral-mediated wild-type p53, antisense to survivin, the mitogen-activated protein kinase inhibitor PD98059, the cyclin-dependent kinase inhibitor Purvalanol A, or the histone deacetylase inhibitor trichostatin A. The radiosensitizing effects of these treatments were determined by clonogenic survival curve analysis and their abilities to suppress survivin expression by Western blot analysis.

RESULTS

All the strategies were shown to radiosensitize A431 cells. This effect correlated with their abilities to downregulate survivin.

CONCLUSION

Expression of survivin appears to confer a radioresistant phenotype that can be overcome using several clinically achievable strategies that target survivin either specifically or nonspecifically.

ErbB receptor tyrosine kinase network inhibition radiosensitizes carcinoma cells

PURPOSE

The expression of epidermal growth factor receptor (EGFR)-CD533, a truncation mutant of the wild-type EGFR, radiosensitizes carcinoma and malignant glioma cell lines. This deletion mutant disrupts EGFR activation and downstream signaling through the formation of inhibitory dimerizations. In this study, the effects of EGFR-CD533 on other ErbB receptor tyrosine kinase (RTK) family members were quantified to better understand the mechanism of EGFR-CD533-mediated radiosensitization.

METHODS AND MATERIALS

Breast carcinoma cell lines with different ErbB RTK expression profiles were transduced with EGFR or ErbB2 deletion mutants (EGFR-CD533 and ErbB2-CD572) using an adenoviral vector. ErbB RTK activation, mitogen activated protein kinase (MAPK) and phosphatidylinositol-3-kinase (PI3K)/p70S6K signaling, and clonogenic survival were determined for expression of each deletion mutant.

RESULTS

EGFR-CD533 radiosensitizes carcinoma cells with either high EGFR expression (MDA-MB231) or low EGFR expression (T47D) through significant blockade of the ErbB RTK network. Analysis of clonogenic survival demonstrate significant enhancement of the alpha/beta ratios, as determined by the linear-quadratic model. Split-dose survival experiments confirm that EGFR-CD533 reduces the repair of cellular damage after ionizing radiation.

CONCLUSION

Expression of EGFR-CD533 inhibits the ErbB RTK network and radiosensitizes carcinoma cells irrespective of the ErbB RTK expression patterns, and ErbB2-CD572 does not radiosensitize cells with low EGFR expression. These studies demonstrate that the mechanism of action for EGFR-CD533-mediated radiosensitization is inhibition of the ErbB RTK network, and is an advantage for radiosensitizing multiple malignant cell types.

Staurosporine modulates radiosensitivity and radiation-induced apoptosis in U937 cells

PURPOSE

The present study aims at investigating the involvement of several genes in the cell cycle distribution and apoptosis in U937 cells, a cell line lacking functional p53 protein, after combined treatment with staurosporine and irradiation.

MATERIALS AND METHODS

Using a DNA fragmentation assay, flow cytometry and western blot analysis, the molecular basis for the effects of staurosporine in combination with the irradiation of leukemia cells was investigated.

RESULTS

Our results indicated that combined treatment led to an increased apoptotic cell death in U937 cells, which is correlated with the phosphorylation of the V-Jun sarcoma virus 17 oncogene homolog (c-JUN) NH(2)-terminal kinase protein (JNK), the activation of caspases, the increase in B cell leukemia/lymphoma 2 (Bcl-2) associated X protein (Bax), the decrease in Bcl xL protein (Bcl-XL) levels, the loss of mitochondria membrane potential and the release of cytochrome c.

CONCLUSIONS

Abrogation of the G2 checkpoint should be an effective strategy against p53-deficient leukemia cells to irradiation-induced cell killing.

Radiosensitization of squamous cell carcinoma by the alkylphospholipid perifosine in cell culture and xenografts

PURPOSE

Combined modality treatment has improved outcome in various solid tumors. Besides classic anticancer drugs, a new generation of biological response modifiers has emerged that increases the efficacy of radiation. Here, we have investigated whether perifosine, an orally applicable, membrane-targeted alkylphospholipid, enhances the antitumor effect of radiation in vitro and in vivo.

EXPERIMENTAL DESIGN

Several long-term and short-term in vitro assays (clonogenic survival, sulforhodamine B cytotoxicity, apoptosis, and cell cycle analysis) were used to assess the cytotoxic effect of perifosine in combination with radiation. In vivo, the response of human KB squamous cell carcinoma xenografts was measured after treatment with perifosine, irradiation, and the combination. Radiolabeled perifosine was used to determine drug disposition in tumor and normal tissues. At various intervals after treatment, tumor specimens were collected to document histopathologic changes.

RESULTS

In vitro, perifosine reduced clonogenic survival, enhanced apoptosis, and increased cell cycle arrest after radiation. In vivo, radiation and perifosine alone induced a dose-dependent tumor growth delay. When combining multiple perifosine administrations with single or split doses of radiation, complete and sustained tumor regression was observed. Histopathologic analysis of tumor specimens revealed a prominent apoptotic response after combined treatment with radiation and perifosine. Radiation-enhanced tumor response was observed at clinically relevant plasma perifosine concentrations and accumulating drug disposition of >100 microg/g in tumor tissue.

CONCLUSIONS

Perifosine enhances radiation-induced cytotoxicity, as evidenced by reduced clonogenic survival and increased apoptosis induction in vitro and by complete tumor regression in vivo. These data provide strong support for further development of this combination in clinical studies.

Hyperacute neuropathological findings after proton beam radiosurgery of the rat hippocampus

OBJECTIVE

To study the hyperacute histological and immunohistochemical effects of stereotactic proton beam irradiation of the rat hippocampus.

METHODS

Nine rats underwent proton beam radiosurgery of one hippocampus with nominal doses of cobalt-2, -12, and -60 Gray equivalents (n = 3 each). Control animals (n = 3) were not irradiated. Animals were killed 5 hours after irradiation and brain sections were stained for Nissl, silver degeneration, deoxyribonucleic acid (DNA) fragmentation (DNAF), and the activated form of two mitogen-activated protein kinases (MAPKs), phospho-Erk1/2 (P-Erk1/2) and p38. Stained cells in the hippocampus expressing DNAF and/or P-Erk1/2 were counted. Confocal microscopy with double immunofluorescent staining was used to examine cellular colocalization of DNAF and P-Erk1/2.

RESULTS

Both DNAF and P-Erk1/2 showed quantitative dose-dependent increases in staining in the targeted hippocampus compared with the contralateral side and controls. This finding was restricted to the subgranular proliferative zone of the hippocampus. Both markers also were up-regulated on the contralateral side when compared with controls in a dose-dependent fashion. Simultaneous staining for DNAF and P-Erk1/2 was found in fewer than half of all cells. p38 was unchanged compared with controls. Although Nissl staining appeared normal, silver stain confirmed dose-dependent cellular degeneration.

CONCLUSION

DNAF, a marker of cell death, was present in rat hippocampi within 5 hours of delivery of cobalt-2 Gray equivalents stereotactically focused irradiation, suggesting that even low-dose radiosurgery has hyperacute neurotoxic effects. Activated mitogen-activated protein kinase was incompletely colocalized with DNAF, suggesting that activation of this cascade is neither necessary nor sufficient to initiate acute cell death after irradiation.

The influence of fractionated radiation therapy on plasma vascular endothelial growth factor (VEGF) concentration in dogs with spontaneous tumors and its impact on outcome

BACKGROUND AND PURPOSE

Vascular endothelial growth factor (VEGF), a specific pro-angiogenic factor is proposed to be involved in cancer progression and resistance to radiation therapy by promoting angiogenesis and by protecting endothelial cells from radiation induced apoptosis. The aim of this study, was first to assess the influence of ionizing radiation on plasma VEGF concentration in spontaneous canine tumors during fractionated radiation therapy with curative or palliative intent and second to analyze plasma VEGF concentration as predictor for treatment outcome.

PATIENTS AND METHODS

For plasma VEGF analysis a human VEGF enzyme linked immunosorbent assay was used. Sixty dogs with various tumor types were included in this study. Dogs were irradiated with either low dose per fx (3-3.5 Gy per fraction, total dose: 42-49 Gy, group A: curative intent) or high dose per fx (6-8 Gy per fraction, total dose: 24-30 Gy, group B: palliative intent). Blood samples were taken before and after dose application at certain time points during therapy. Follow-up evaluation was performed for analysis of time to treatment failure and survival.

RESULTS

Repeated measures analysis showed no increase of plasma VEGF in dogs treated with fractionated radiation therapy (group A and B). Dichotomizing baseline plasma VEGF into two groups with high and low plasma VEGF, resulted in shorter time to treatment failure in dogs with high plasma VEGF levels (TTF, group A: P=0.038, group B: P=0.041).

CONCLUSIONS

This study demonstrated that dogs with a plasma VEGF level higher than 5 pg/ml had a poorer outcome after radiation therapy. It is therefore, suggested, to use plasma VEGF as predictor for treatment outcome in radiation therapy.

Effect of Ionizing Radiation on Rat Tissue: Proteomic and Biochemical Analysis

Reactive oxygen species (ROS), generated by ionizing radiation, has been implicated in its effect on living tissues. We confirmed the changes in the oxidative stress markers upon irradiation. We characterized the changes in the proteome profile in rat liver after administering irradiation, and the affected proteins were identified by MALDI-TOF-MS and ESI-MS/MS. The identified proteins represent diverse sets of proteins participating in the cellular metabolism. Our results demonstrated that proteomics analysis is a useful method for characterization of a global proteome change caused by ionizing radiation to unravel the molecular mechanisms involved in the cellular responses to ionizing radiation.

Conjugated bile acids promote ERK1/2 and AKT activation via a pertussis toxin-sensitive mechanism in murine and human hepatocytes

Several studies have argued that G-protein-coupled receptors (GPCR) have the capacity to promote activation of receptor tyrosine kinases. The current studies were performed to examine the regulation of the extracellular regulated kinase (ERK)1/2 and AKT pathways by conjugated and unconjugated bile acids in primary hepatocytes. Deoxycholic acid (DCA), chenodeoxycholic acid (CDCA), taurodeoxycholic acid (TDCA), glycodeoxycholic acid (GDCA), taurochenodeoxycholic acid (TCDCA), glycochenodeoxycholic acid (GCDCA), taurocholic acid (TCA), glycocholic acid (GCA), and tauroursodeoxycholic acid (TUDCA) all activated ERK1/2 in primary rat hepatocytes that was abolished by inhibition of ERBB1, and significantly reduced by ROS quenching agents. Bile acid-induced AKT activation was blunted by preventing ERBB1 activation and ROS generation. Treatment of rat hepatocytes with pertussis toxin (PTX) did not alter ERK1/2 and AKT activation induced by DCA or CDCA but abolished pathway activations by conjugated bile acids. Similar data to those with PTX were obtained when a dominant negative form of G(i1alpha) was overexpressed. Treatment of rat hepatocytes with TDCA and TCA promoted guanosine triphosphate (GTP) loading of G(i1alpha), G(i2alpha), and G(i3alpha) in vitro. Treatment of rat hepatocytes with PTX abolished TDCA-induced tyrosine phosphorylation of ERBB1. Similar findings to those in rat hepatocytes were also obtained in primary mouse and human hepatocytes, but not in established rodent or human hepatoma cell lines. In conclusion, collectively our findings demonstrate that unconjugated bile acids activate hepatocyte receptor tyrosine kinases and intracellular signaling pathways in a ROS-dependent manner. In contrast, conjugated bile acids primarily activate receptor tyrosine kinases and intracellular signaling pathways in a GPCR (G(ialpha))-dependent and ROS-dependent manner.

Inhibition of insulin/IGF-1 receptor signaling enhances bile acid toxicity in primary hepatocytes

Modulation of ERBB and insulin-like growth factor 1 (IGF-1) receptor function is recognized as a potential mechanism to inhibit tumor growth. We and others have shown that inhibition of ERBB1 can enhance bile acid toxicity. Herein, we extend our analyses to examine the impact of insulin/IGF-1 receptor inhibition on primary hepatocyte survival when exposed to the secondary bile acid deoxycholic acid (DCA) and compare the impact inhibition of this receptor has on bile acid toxicity effects to that of ERBB1/MEK1/2 inhibition. The insulin/IGF-1 receptor inhibitor NVP-ADW742 at concentrations which inhibit both the insulin and IGF-1 receptors had a modest negative impact on hepatocyte viability, and strongly potentiated DCA-induced apoptotic cell death. Identical data were obtained expressing a dominant negative IGF-1 receptor in hepatocytes; a receptor which acts to inhibit both the IGF-1 receptor and the insulin receptor in trans. Inhibition of ERBB1 function using Iressa (gefitinib) or the tyrphostin AG1478 had more modest effects at enhancing DCA lethality than inhibition of the insulin/IGF-1 receptor function. In contrast, over-expression of a dominant negative ERBB1 protein had pleiotropic effects on multiple signaling pathways in an apparently non-specific manner. These findings suggest that novel therapeutic kinase inhibitors, targeted against growth factor receptors, have the potential to promote bile acid toxicity in hepatocyte when bile flow may be impaired.

Repopulation of cancer cells during therapy: an important cause of treatment failure

Radiotherapy and chemotherapy are given in multiple doses, which are spaced out to allow the recovery of normal tissues between treatments. However, surviving cancer cells also proliferate during the intervals between treatments and this process of repopulation is an important cause of treatment failure. Strategies developed to overcome repopulation have improved clinical outcomes, and now new strategies to inhibit repopulation are emerging in parallel with advances in the understanding of underlying biological mechanisms.

Prognostic impact of epidermal growth factor receptor (EGFR) expression on loco-regional recurrence after preoperative radiotherapy in rectal cancer

BACKGROUND

Epidermal growth factor receptor (EGFR) represents a major target for current radiosensitizing strategies. We wished to ascertain whether a correlation exists between the expression of EGFR and treatment outcome in a group of patients with rectal adenocarcinoma who had undergone preoperative radiotherapy (RT).

METHODS

Within a six-year period, 138 patients underwent preoperative radiotherapy and curative surgery for rectal cancer (UICC stages II-III) at our institute. Among them, 77 pretherapeutic tumor biopsies were available for semi-quantitative immunohistochemical investigation evaluating the intensity and the number (extent) of tumor stained cells. Statistical analyses included Cox regression for calculating risk ratios of survival endpoints and logistic regression for determining odds ratios for the development of loco-regional recurrences.

RESULTS

Median age was 64 years (range: 30-88). Initial staging showed 75% and 25% stage II and III tumors, respectively. RT consisted of 44-Gy pelvic irradiation in 2-Gy fractions using 18-MV photons. In 25 very low-rectal-cancer patients the primary tumor received a boost dose of up to 16 Gy for a sphincter-preservation approach. Concomitant chemotherapy was used in 17% of the cases. All patients underwent complete total mesorectal resection. Positive staining (EGFR+) was observed in 43 patients (56%). Median follow-up was 36 months (range: 6-86). Locoregional recurrence rates were 7 and 20% for EGFR extent inferior and superior to 25%, respectively. The corresponding locoregional recurrence-free survival rate at two years was 94% (95% confidence interval, CI, 92-98%) and 84% (CI 95%, 58-95%), respectively (P = 0.06). Multivariate analyses showed a significant correlation between the rate of loco-regional recurrence and three parameters: EGFR extent superior to 25% (hazard ratio = 7.18, CI 95%, 1.17-46, P = 0.037), rectal resection with microscopic residue (hazard ratio = 6.92, CI 95%, 1.18-40.41, P = 0.032), and a total dose of 44 Gy (hazard ratio = 5.78, CI 95%, 1.04-32.05, P = 0.045).

CONCLUSION

EGFR expression impacts on loco-regional recurrence. Knowledge of expression of EGFR in rectal cancer could contribute to the identification of patients with an increased risk of recurrences, and to the prediction of prognosis.

Inhibition of the type III epidermal growth factor receptor variant mutant receptor by dominant-negative EGFR-CD533 enhances malignant glioma cell radiosensitivity

PURPOSE

The commonly expressed variant epidermal growth factor receptor (EGFR), the type III EGFR variant (EGFRvIII), functions as an oncoprotein promoting neoplastic transformation and tumorigenicity. The role of EGFRvIII in cellular responses to genotoxic stress, such as ionizing radiation, is only minimally defined. Thus, we have investigated EGFRvIII as a potential modulator of cellular radiation responses and explored the feasibility of adenovirus (Ad)-mediated expression of dominant-negative EGFR-CD533 as a gene therapeutic approach for inhibiting EGFRvIII function in vitro and in vivo.

EXPERIMENTAL DESIGN AND RESULTS

EGFR-CD533 and EGFRvIII were expressed in vitro and in vivo in malignant U-373 MG glioma cells through transduction with an Ad vector, Ad-EGFR-CD533 and Ad-EGFRvIII, respectively. In vivo studies defined the importance of EGFRvIII as a modulator of radiation responses, demonstrating a 2.6-fold activation of EGFRvIII in U-373 malignant glioma tumors. Concomitant expression of EGFR-CD533 inhibited the radiation-induced activation of EGFRvIII in vitro and completely abolished the enhanced clonogenic survival conferred by EGFRvIII. The ability of EGFR-CD533 to inhibit EGFRvIII function was further confirmed in vivo through complete inhibition of EGFRvIII-mediated increased tumorigenicity and radiation-induced activation of EGFRvIII. Growth delay assays with U-373 xenograft tumors demonstrated that the expression of EGFR-CD533 significantly enhanced radiosensitivity of tumor cells under conditions of intrinsic and Ad-mediated EGFRvIII expression.

CONCLUSIONS

We conclude that EGFRvIII confers significant radioresistance to tumor cells through enhanced cytoprotective responses, and we have demonstrated that dominant-negative EGFR-CD533 effectively inhibits EGFRvIII function. These data affirm the broad potential of EGFR-CD533 to radiosensitize human malignant glioma cells.

Differential radiosensitisation by ZD1839 (Iressa), a highly selective epidermal growth factor receptor tyrosine kinase inhibitor in two related bladder cancer cell lines

The epidermal growth factor receptor (EGFR) is expressed in a wide variety of epithelial tumours including carcinoma of the bladder. Stimulation of the EGFR pathway is blocked by ZD1839 (Iressa), a highly selective EGFR tyrosine kinase inhibitor. Radical radiotherapy is an established organ sparing treatment option for muscle invasive bladder cancer and this study has explored the possibility for the use of ZD1839 as a radiosensitiser in this scenario. The effect of combination treatment with ZD1839 (0.01 μM) and ionising radiation in the established bladder cancer cell lines MGH-U1 and its radiosensitive mutant clone S40b was measured by clonogenic assays. A highly significant radiosensitising effect was seen in both cell lines (P<0.001 for MGH-U1 and S40b cell lines). This effect was independent of the concentration of the drug and the duration of exposure prior to treatment with ionising radiation. Cell cycle kinetics of both cell lines was not significantly altered with ZD1839 (0.01 μM) as a single agent. A modest induction of apoptosis was observed with ZD1839 (0.01 μM) as a single agent, but a marked induction was observed with the combination treatment of ZD1839 and ionising radiation. These results suggest a potentially important role for ZD1839 in combination with radiotherapy in the treatment of muscle invasive bladder cancer.

Novel targeted agents in the treatment of lung cancer

Lung cancer is the leading cause of cancer-related mortality in the US. Although an improvement in outcome is possible with the continued advancement of cytotoxic-based treatment, clinical research is currently focused on utilising novel molecular targets with proven efficacy in preclinical models and a low toxicity profile. This is the result of advances in understanding of tumour biology and molecular pathways that have been implicated in cancer pathogenesis and progression. Novel agents targeting cell cycle regulation, angiogenesis and signal transduction pathways have reached clinical testing in lung cancer and are discussed in this review.